Just out of interest, did it only start slipping after you (or rather your mechanic) changed the oil?

Not done the clutch on the Z, but done a fair few wet clutches over the years and they’re all fundamentally the same. If it’s slipping then it’ll either by poorly adjusted (no free play), contaminated, swollen or worn plates or weak springs. The thing that raises an eyebrow, is that most of the previous tend to cause slippage to gradually appear and worsen over time, they don’t often suddenly happen. It’s probably worth checking with your man whether he used the “good” oil and not an API “energy conserving” low friction car oil, which is a nightmare for wet clutches, causing slip almost the moment it’s used. Maybe you were just showing off and riding it harder in top at the Dragon so it became apparent?!

One thing worth checking before you start throwing money at a clutch rebuild is the cable. I have come across clutch slip cause by frayed cables before. What happens is the cable will pull smoothly when the lever is squeezed releasing the clutch fully, but won’t return fully because of the fray catching somewhere, either inside the outer, or more usually at either end where the cable emerges. The funny thing is, when this scenario occurs you end up with more free play than normally as the clutch operating arm cannot return fully, so all seems well even though it isn’t. You can't often tell just looking, you need to unhook the cable at both ends and see if it glides smoothly through the outer.

The plates are (as you’ve discovered) relatively cheap, and they’re pretty simple to replace as are the springs, so if you’ve ruled out maladjustment and cable issues, then you may as well replace the lot. Either way, if the plates are contaminated (by low friction additives), swollen (usually from excess heat), worn or the springs have gone west then the only solution is replacement. The rest of the clutch mechanism and basket you can inspect when you disassemble the clutch. I personally wouldn’t bother with HD springs, I’ve used them in the past with no discernible difference other than a stiffer clutch action! Unless you’re running serious horsepower, I’d stick with the stock springs, they’re more than up to the job when in good nick and save your money.

Here’s a couple of other threads that may be of use?

http://www.xt660.com/showthread.php?t=20931

http://www.xt660.com/showthread.php?t=16953

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